Agricultural system

ABSTRACT

A hydraulic control system for controlling the down force on an agricultural implement comprises a hydraulic cylinder containing a movable ram, a source of pressurized fluid coupled to the hydraulic cylinder on a first side of the ram by a first controllable valve, a fluid sump coupled to the hydraulic cylinder on the first side of the ram by a second controllable valve, and an electrical controller coupled to the valves for opening and closing the valves. The valves may be self-latching valves that remain in an open or closed position until moved to the other position in response to a signal from the controller.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims priority to U.S. patentapplication Ser. No. 14/858,171, filed Sep. 18, 2015, now allowed, whichis a continuation-in-part of and claims priority to U.S. patentapplication Ser. No. 14/593,492, filed Jan. 9, 2015, now U.S. Pat. No.9,681,601, U.S. Provisional Application No. 62/085,334, filed Nov. 28,2014; and U.S. Provisional Application No. 62/076,767, filed Nov. 7,2014, each of which is hereby incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

This invention relates generally to agricultural planters and, moreparticularly, to gauge wheel load sensors and down pressure controlsystems for agricultural planters.

BRIEF SUMMARY

In accordance with one embodiment, a hydraulic control system forcontrolling the down force on an agricultural implement comprising ahydraulic cylinder containing a movable ram, a source of pressurizedfluid coupled to the hydraulic cylinder on a first side of the ram by afirst controllable valve, a fluid sump coupled to the hydraulic cylinderon the first side of the ram by a second controllable valve, and anelectrical controller coupled to the valves for opening and closing thevalves. The valves are preferably self-latching valves, such as magneticlatching valves, that remain in an open or closed position until movedto the other position in response to a signal from the controller.Alternatively, the valves may be non-latching valves that arespring-biased toward their closed positions. A pair of energy storagedevices, such as accumulators, may be coupled to the cylinder onopposite sides of the ram. A pressure transducer is preferably coupledto the cylinder on one side of the ram. A pair of check valves maycouple the cylinder to the energy storage device and to the controllablevalves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical longitudinal section through a portion of anagricultural planter that includes a gauge wheel and an opener device.

FIG. 2 is an enlargement of the left side of FIG. 1.

FIG. 3 is a bottom perspective of the control portion of the equipmentshown in FIG. 1.

FIG. 4 is an enlarged side elevation of the equipment shown in FIG. 3.

FIG. 5 is an enlarged top plan view of the equipment shown in FIG. 3.

FIG. 6 is an enlarged vertical longitudinal section through theequipment shown in FIG. 3.

FIG. 7 is a plan view of a gauge wheel transducer system for anagricultural planter that includes a gauge wheel and an opener device.

FIG. 8 is a side elevation of the transducer system shown in FIG. 7.

FIG. 9 is a sectional view taken along line A-A in FIG. 7.

FIG. 10 is a side elevation, partially in section, of the transducersystem of FIGS. 7-9 mounted on a gauge wheel and its supportingstructure.

FIG. 11 is a perspective view of portions of the devices shown in FIG.10.

FIG. 12 is a plan view similar to FIG. 7 but with portions removed toshow the equalizer arm.

FIG. 13 is a plan view of a modified transducer system.

FIG. 14 is a longitudinal section taken along line 14-14 in FIG. 13.

FIG. 15A is a side elevation of a modified sensing system for detectingthe pressure exerted on a pair of gauge wheels.

FIG. 15B is an end elevation of the system shown in FIG. 15A.

FIG. 16 is a schematic diagram of a hydraulic and electrical controlsystem for controlling a down pressure actuator.

FIG. 17 is a schematic diagram of a first modified hydraulic andelectrical control system for controlling a down pressure actuator.

FIG. 18 is a schematic diagram of a second modified hydraulic andelectrical control system for controlling a down pressure actuator.

FIG. 19 is a schematic diagram of a third modified hydraulic andelectrical control system for controlling a down pressure actuator.

FIG. 20 is a perspective view of a planting row unit adapted to beattached to a towing frame.

FIG. 21 is an enlarged perspective view of the down-pressure controlassembly in the row unit of FIG. 20;

FIG. 22 is the same perspective view shown in FIG. 16, rotated 90degrees in a clockwise direction;

FIG. 23 is an enlarged side elevation of the control assembly shown inFIGS. 21 and 22, from the left side of the assembly as shown in FIG. 21.

FIG. 24 is a section taken along line 19-19 in FIG. 23.

FIG. 25 is a side elevation of the right side of the control assemblyshown in FIG. 23.

FIG. 26 is a side elevation of the right side of the control assemblyshown in FIG. 25.

FIG. 27 is a section taken along line 22-22 in FIG. 25.

FIG. 28 is a section taken along line 23-23 in FIG. 25.

FIG. 29 is an enlarged exploded perspective of the central portion ofthe left side of the control assembly shown in FIG. 21.

FIG. 30 is a horizontal section taken through the two ports shown inFIG. 29, with all the parts assembled.

FIG. 31 is a vertical section taken through the middle of the controlassembly shown in FIG. 7, with the rod of the hydraulic cylinder in itsfully extended position.

FIG. 32 is the same vertical section shown in FIG. 21, with the rod ofthe hydraulic cylinder in an intermediate position.

FIG. 33 is the same vertical section shown in FIG. 21, with the rod ofthe hydraulic cylinder in its fully retracted position.

FIG. 34A is a schematic diagram of a hydraulic and electrical controlsystem for use in the device of FIGS. 20-33 to provide rebound damping.

FIG. 34B is a schematic diagram of a modified hydraulic and electricalcontrol system for use in the device of FIGS. 20-33 to provide bothrebound and compression damping.

FIG. 35A is a schematic diagram of a modified hydraulic and electricalcontrol system for use in the device of FIGS. 14-33 to provide rebounddamping.

FIG. 35B is a schematic diagram of another modified hydraulic andelectrical control system for use in the device of FIGS. 14-33 toprovide both rebound and compression damping.

FIG. 36 is a waveform diagram illustrating different modes of operationprovided by a PWM control system for the hydraulic valves in the systemof FIG. 34B.

DETAILED DESCRIPTION

An agricultural planter typically includes a number of individual rowunits, each of which includes its own row cleaner device, row openerdevice and row closing device. The down pressure is typically controlledseparately for each row unit or each of several groups of row units, andis preferably controlled separately for one or more of the individualdevices in each row unit, as described in more detail in pending U.S.application Ser. No. 14/146,822 filed Jan. 3, 2014, which isincorporated by reference herein in its entirety.

FIGS. 1-6 illustrate an improved gauge wheel load sensor that takes theupward force from a pivoting planter gauge wheel support, such as thepivoting support arms 10 in the row unit equipment shown in FIGS. 1 and2, and translates that force into a fluid pressure in a fluid chamber11. The gauge wheel support arms push against an equalizer support 12,which is connected via a pivot 13 with a rocker/cam 14. The force on thegauge wheel due to the weight of the row unit and applied down forcecauses the rocker/cam 14 to pivot around a pivot bolt 15 and pushagainst a hydraulic ram 16. This force on the ram 16 causes the fluid inthe chamber 11 to pressurize. The pressure is proportional to the amountof gauge wheel load. A pressure transducer 18 reads the amount ofpressure and sends a signal to a row unit down pressure controller viasignal line 19. This signal allows the planter row unit down pressure tobe controlled to a desired level.

Depth adjustment is accomplished in the conventional sense by pivotingthe assembly around a pivot 20, and locking a handle 21 into the desiredposition with a mechanism 22. With this design it is imperative thatthat there is no air trapped in the fluid chamber 11. For this reasonthe mechanism includes a bleed valve 23. The process for removal of airis to extend the ram to the maximum extent with calibration/travellimiter plates 24 (FIG. 4) removed. The system is then filled completelywith fluid with the bleed valve 23 closed. Then the bleed valve 23 isopened, and the rocker arm 14 is pushed against the ram 16 to move theram to the exact place where the calibration/travel limit plates 24allow a calibration plate retaining screw 25 to fit into a hole. Thisensures that each assembly is set the same so all the row units of theplanter are at the same depth. At this point the bleed valve 23 isclosed. With all air removed, the mechanical/fluid system will act as arigid member against forces in compression. The travel limiter plate 24keeps a cam pivot weldment 27 from falling down when the planter islifted off the ground.

Standard industry practice is to use a strain gauge to directly measurethe planter gauge wheel load. The design shown in FIGS. 1-6 is animprovement over the state of the art because it allows the sensor tomeasure only the down force on the gauge wheels. In typical designsusing strain gauge type sensors, the mechanical linkage that allows thegauge wheels to oscillate causes the measured wheel force to havesubstantial noise due to changes in the force being applied. For thisreason it can be difficult to determine which parts of the signalcorrespond to actual changes in down force on the gauge wheels, versussignal changes that are due to movement of components of the gauge wheelsupport mechanism. The reason for this is that strain gauge sensors willonly measure the force that is being applied in a single plane. Becauseof the linkage and pivot assembly that is used on typical planters, theforce being applied to the strain gauge type designs can change based onthe depth setting or whether the planter gauge wheels are oscillatingover terrain. In this way they will tend to falsely register changes ingauge wheel down force and make it difficult to have a closed loop downpressure response remain consistent.

Additionally, the fluid seal of the pressure sensor creates friction inthe system which has the effect of damping out high frequency noise.Agricultural fields have very small scale variations in the surfacewhich causes noise to be produced in the typical down force sensorapparatus. By using fluid pressure this invention decouples the sensorfrom the mechanical linkage and allows the true gauge wheel force to bemore accurately measured. Lowering the amount of systematic noise in thegauge wheel load output sensor makes it easier to produce an automaticcontrol system that accurately responds to true changes in the hardnessof the soil as opposed to perceived changes in soil hardness due tonoise induced on the sensor.

FIGS. 7-12 illustrate a modified gauge wheel load sensor that includesan integrated accumulator 125. The purpose of the accumulator 125 is todamp pressure spikes in the sensor when the planter is operating at lowgauge wheel loads. When the forces that the gauge wheel support arms 110are exerting on the hydraulic ram 117 are near zero, it is more commonfor the surface of the soil or plant residue to create pressure spikesthat are large in relation to the desired system sensor pressure. As thetarget gauge wheel down force increases, and consequently the pressurein the fluid chamber 111 and the transducer output voltage from sensor118, the small spikes of pressure due to variation in the soil surfaceor plant residue decreases proportionally.

In the present system, rather than have a perfectly rigid fluid couplingbetween the ram 117 and the pressure transducer 118, as load increaseson the ram 117, the fluid first pushes against an accumulator 122 thatis threaded into a side cavity 123 in the same housing that forms themain cavity for the ram 117, compressing an accumulator spring 126 untilthe piston 125 rests fully against a shoulder on the interior wall ofthe accumulator housing 127, thus limiting the retracting movement ofthe accumulator piston 125. At this point, the system becomes perfectlyrigid. The amount of motion permitted for the accumulator piston 125must be very small so that it does not allow the depth of the gaugewheel setting to fluctuate substantially. The piston accumulator (orother energy storage device) allows the amount of high frequency noisein the system to be reduced at low gauge-wheel loads. Ideally anautomatic down pressure control system for an agricultural plantershould maintain a down pressure that is as low as possible to avoid overcompaction of soil around the area of the seed, which can inhibit plantgrowth. However, the performance of most systems degrades as the gaugewheel load becomes close to zero, because the amount of latent noiseproduced from variation in the field surface is large in relation to thedesired gauge wheel load.

Planter row units typically have a gauge wheel equalizer arm 130 that isa single unitary piece. It has been observed that the friction betweenthe equalizer arm 130 and the gauge wheel support arms 110, as the gaugewheel 115 oscillates up and down, can generate a substantial amount ofnoise in the sensor. At different adjustment positions, the edges of theequalizer arm 130 contact the support arms 10 at different orientationsand can bite into the surface and prevent forces from being smoothlytransferred as they increase and decrease. When the equalizer arm 130 isa single unitary piece, there is necessarily a high amount of frictionthat manifests itself as signal noise in the sensor. This signal noisemakes it difficult to control the down pressure system, especially atlow levels of gauge wheel load.

To alleviate this situation, the equalizer arm 130 illustrated in FIG.13 has a pair of contact rollers 131 and 132 are mounted on oppositeends of the equalizer arm. These rollers 131 and 132 become theinterface between the equalizer arm and the support arms 110, allowingforces to be smoothly transferred between the support arms 110 and theequalizer arm 130. The roller system allows the gauge wheel support arms110 to oscillate relative to each other without producing any slidingfriction between the support arms 110 and the equalizer arm 130. Thissignificantly reduces the friction that manifests itself as signal noisein the sensor output, which makes it difficult to control the downpressure control system, especially at low levels of gauge wheel load.

FIG. 14 is a longitudinal section through the device of FIG. 13, withthe addition of a rocker arm 150 that engages a ram 151 that controlsthe fluid pressure within a cylinder 152. A fluid chamber 153 1 adjacentthe inner end of the ram 151 opens into a lateral cavity that contains apressure transducer 154 that produces an electrical output signalrepresenting the magnitude of the fluid pressure in the fluid chamber153. The opposite end of the cylinder 152 includes an accumulator 155similar to the accumulator 125 included in the device of FIG. 9described above. Between the fluid chamber 153 and the accumulator 155,a pair of valves 156 and 157 are provided in parallel passages 158 and159 extending between the chamber 153 and the accumulator 155. The valve156 is a relief valve that allows the pressurized fluid to flow from thechamber 153 to the accumulator 155 when the ram 151 advances fartherinto the chamber 153. The valve 157 is a check valve that allowspressurized fluid to flow from the accumulator 155 to the chamber 153when the ram 151 moves outwardly to enlarge the chamber 153. The valves156 and 157 provide overload protection (e.g., when one of the gaugewheels hits a rock) and to ensure that the gauge wheels retain theirelevation setting.

FIGS. 15A and 15B illustrate a modified sensor arrangement for a pair ofgauge wheels 160 and 161 rolling on opposite sides of a furrow 162. Thetwo gauge wheels are independently mounted on support arms 163 and 164connected to respective rams 165 and 166 that control the fluid pressurein a pair of cylinders 167 and 168. A hydraulic hose 169 connects thefluid chambers of the respective cylinders 167 and 168 to each other andto a common pressure transducer 170, which produces an electrical outputsignal corresponding to the fluid pressure in the hose 169. The outputsignal is supplied to an electrical controller that uses that signal tocontrol the down forces applied to the two gauge wheels 160 and 161. Itwill be noted that the two gauge wheels can move up and downindependently of each other, so the fluid pressure sensed by thetransducer 170 will be changed by vertical movement of either or both ofthe gauge wheels 160 and 161.

FIGS. 16-19 illustrate electrical/hydraulic control systems that can beused to control a down-pressure actuator 180 in response to theelectrical signal provided to a controller 181 by a pressure transducer182. In each system the transducer 182 produces an output signal thatchanges in proportion to changes in the fluid pressure in a cylinder 183as the position of a ram 184 changes inside the cylinder 183. In FIG.16, the pressurized fluid chamber in the cylinder 183 is coupled to anaccumulator 185 by a relief valve 186 to allow pressurized fluid to flowto the accumulator, and by a check valve 187 to allow return flow ofpressurized fluid from the accumulator to the cylinder 183. In FIG. 17,the accumulator 185 is replaced with a pressurized fluid source 188connected to the check valve 187, and a sump 189 connected to the reliefvalve 186. In FIG. 18, the accumulator 185 is connected directly to thepressurized fluid chamber in the cylinder 183, without any interveningvalves. In the system of FIG. 19, the pressure sensor 182 is connecteddirectly to the pressurized fluid chamber in the cylinder 183.

FIG. 20 illustrates a planting row unit 210 that includes afurrow-opening device 211 for the purpose of planting seed or injectingfertilizer into the soil. A conventional elongated hollow towing frame(typically hitched to a tractor by a draw bar) is rigidly attached tothe front frame 212 of a conventional four-bar linkage assembly 213 thatis part of the row unit 210. The four-bar (sometimes referred to as“parallel-bar”) linkage assembly 213 is a conventional and well knownlinkage used in agricultural implements to permit the raising andlowering of tools attached thereto.

As the planting row unit 210 is advanced by the tractor, the openingdevice 211 penetrates the soil to form a furrow or seed slot. Otherportions of the row unit 210 then deposit seed in the seed slot andfertilizer adjacent to the seed slot, and close the seed slot bydistributing loosened soil into the seed slot with a pair of closingwheels. A gauge wheel 214 determines the planting depth for the seed andthe height of introduction of fertilizer, etc. Bins 215 on the row unitcarry the chemicals and seed which are directed into the soil. Theplanting row unit 210 is urged downwardly against the soil by its ownweight, and, in addition, a hydraulic cylinder 216 is coupled betweenthe front frame 212 and the linkage assembly 213 to urge the row unit210 downwardly with a controllable force that can be adjusted fordifferent soil conditions. The hydraulic cylinder 216 may also be usedto lift the row unit off the ground for transport by a heavier,stronger, fixed-height frame that is also used to transport largequantities of fertilizer for application via multiple row units.

The hydraulic cylinder 216 is shown in more detail in FIGS. 21-33.Pressurized hydraulic fluid from the tractor is supplied by a hose 301to a port 304 that leads into a matching port of a unitary housing 223that forms a cavity 224 of a hydraulic cylinder containing a hollow rod225. The housing 223 also forms a side port 226 that leads into a secondcavity 227 that contains hydraulic fluid that can be used to control thedown pressure on the row unit, as described in more detail below.

The hydraulic control system includes a pair of controllable 2-wayhydraulic lines 301 and 302 leading to the hydraulic cylinder in theunitary housing 223, which includes an integrated electronic controller303. The hydraulic lines 301 and 302 are coupled to a pressure/inletvalve and a return outlet valve which are controlled by signals from thecontroller 303. The controller 303 receives input signals from apressure transducer 304 that senses the pressure in the cavity 224, anda gauge wheel sensor that monitors the elevation of a tool relative tothe elevation of the gauge wheel.

Slidably mounted within the hollow interior of the rod 225 is adown-pressure accumulator piston 230, which forms one end of a sealedchamber 231 containing pressurized gas that is part of the down-pressureaccumulator. The lower end of the chamber 231 is sealed by a rod end cap232 that contains a valve 233 for use in filling the chamber 231 withpressurized gas. Thus, the down-pressure accumulator is formed entirelywithin the hollow rod 225.

The hydraulic pressure exerted by the hydraulic fluid on the end surfaceof the rod 225 and the accumulator piston 230 urges the rod 225downwardly, with a force determined by the pressure of the hydraulicfluid and the area of the exposed end surfaces of the rod 225 and thepiston 230. The hydraulic fluid thus urges the rod 225, and thus the rowunit, in a downward direction, toward the soil.

When an upward force is exerted on the rod 225, such as when a rock orincreased soil hardness is encountered, the rod 225 is moved upwardlywithin the cavity 224, as depicted in FIGS. 32 and 33. Because thecavity 224 is filled with pressurized hydraulic fluid in the cavity 224,the accumulator piston 230 does not move upwardly with the rod 225, asdepicted in FIGS. 32 and 33. Thus, the pressurized gas between theaccumulator piston 230 and the cap 232 at the lower end of the rod 225is further compressed. This process continues as the rod 25 movesupwardly within the cavity 224, until the upper end of the rod engagesthe housing 216, as depicted in FIG. 33. In this fully retractedposition of the rod 225, the accumulator piston 230 engages the end cap232 on the lower end of the rod 225.

During upward movement of the rod 225 and downward movement of theaccumulator piston 230, hydraulic fluid flows from the second cavity 227through the conduit 226 into the space between the outer surface of therod 225 and the wall of the cavity 224. The hydraulic fluid if urged inthis direction by a second accumulator formed by a piston 240 and acharge of pressurized gas between the piston 240 and an end cap 241 thatseals the top of the cavity 227. As can be seen in FIGS. 32 and 33, thecompressed gas urges the piston 240 downwardly as the rod 225 movesupwardly, thus forcing hydraulic fluid from the cavity 227 through acheck valve 228 into the increasing space between the outer surface ofthe rod 225 and the wall of the cavity 224. In FIG. 33, the rod 225 hasbeen withdrawn to its most retracted position, and the accumulatorpiston 240 has moved to its lowermost position where it engages thebottom end wall of the cavity 227. At this point, the row unit is in itsuppermost position.

The process is reversed when the rod 225 returns to its extendedposition, with the accumulators providing dynamic “rebound” dampingduring this return movement. As the rod 225 moves downwardly, hydraulicfluid is returned to the cavity 227 through a restriction 229 to dampthe downward movement of the rod. The restriction 229 can be adjusted byturning the screw formed by the outer end portion of the tapered pin 229a that forms the restriction 229. The return flow rate of the hydraulicfluid is also affected by the pressure of the gas in the space above theaccumulator piston 240, which must be overcome by the returninghydraulic fluid to move the piston 40 upwardly.

It will be appreciated that the system described above does not requireany hydraulic fluid to flow into or out of the housing 223 duringadvancing and retracting movement of the rod 225 that controls thevertical position of the row unit relative to the soil. Thus, there isno need to open or close any valves to control the flow of hydraulicfluid in and out of the tractor reservoir of hydraulic fluid. This isnot only more efficient than moving hydraulic fluid to and from the mainreservoir, but also makes the operation of the row unit much smoother,which in turn improves the delivery of seed and/or fertilizer to thedesired locations in the soil. The actuator assembly is normally closedwith no fluid entering or leaving the actuator/accumulator assemblyunless one or more valves are opened. There is also an advantage inusing two valves because a 2-position, 1-way valve can be madefast-acting more readily that a 3-position, 2-way valve. Moreover, thecomputer controller can be directly integrated into the actuatorassembly. The single double-acting actuator with two accumulators, oneacting in the downward direction and one acting in the upward direction,can be mounted in the same location as previous actuators used on rowunits.

The present system has an accumulator on both sides of the actuator,with valves that control flow, not pressure, so that the actuator canbecome a totally closed system with no oil entering or leaving. Thecompensator design is linear because the piston accumulator is packagedwithin the inner diameter of the ram of a larger cylinder, which reducesthe number of parts as well as the size of the actuator unit. The linearcompensator design allows perfectly open and unrestricted flow of oil inthe compression direction, which is advantageous because of the need torapidly absorb energy when the row unit hits a rock or obstacle.

When the valves have a “latching” feature, the spools of the valves canbe rapidly magnetized and demagnetized. This allows the valve to latchmagnetically in either the open or closed condition so that the valvedoes not consume power continuously, as a typical proportional coilvalve does. Moreover, the latching valve design takes advantage of theability of the accumulators to allow the planter linkage to float up anddown without requiring any gain or loss of fluid. Rather, the downpressure on the planter may be changed by holding either the pressure orreturn valve open for varying pulse width modulated durations to achievea rise or drop in down pressure. These valves may have a very fast rateof change between open and closed conditions. If the valve changes statevery quickly, typically less than 10 milliseconds, and requires no powerto remain either open or closed, it is possible to achieve negligiblepower consumption system because the probability that any two valveswill be in the process of opening or closing at the exact same time isvery low.

Planter row units have varying unsprung weights (the portion of theplanter row unit weight that is carried by the gauge wheels and not theframe). In some tillage and soil conditions which are very soft or proneto compaction, it can be advantageous to suspend some or all of thisweight by pushing upward against it.

By pressurizing the uplift accumulator by filling gas through the gasvalve, the gas pressure increases, pushing the piston accumulatoragainst the fluid which is connected to the main cylinder by a fluidpassageway. This pressure exerts an upward force on the smaller crosssectional area of the rod side of the main piston seals, and the gaspressure can be adjusted to change the amount of uplift force. It isalso possible to have a gas pressure system that allows remoteadjustment of the gas pressure. The fluid in the uplift circuit forms aclosed system, and a manual or automatic flow control valve can be addedbetween the main cylinder and the uplift accumulator to restrict flow,causing damping of the rebound cycle of the suspension cylinder.

Fluid is introduced into the cylinder by opening the pressure valve forsome duration of time, allowing high-pressure fluid from the tractor toflow into the fluid chamber. This high-pressure fluid pushes against thelinear compensator accumulator piston, which in turn compresses the gasto equalize the pressures on opposite sides of the piston. Theaccumulator piston will move back and forth inside the hollow rod whenthe down pressure is changing, even if the rod is not moving up anddown. The length of time the pressure valve remains open corresponds tothe size of the adjustment needed. Control is being accomplished in aclosed loop fashion based on the planter gauge wheel load. Once therequired pressure is achieved, the valve closes so that the actuator isa closed system again. The actuator can then allow the row unit to floatup and down, compressing and decompressing the gas in the down-pressureand up-pressure accumulators. This will generate heat in the process—theheat is energy that is being damped from the system. To facilitate theremoval of this heat from the system, the portion of the housing 223that forms the cavity 227 forms multiple cooling fins 242 around itsexterior surface.

FIG. 34A is a schematic diagram of a hydraulic control system that usesa single hydraulic cylinder 1601, two two-position control valves 1602,1603 and a pair of accumulators 1604, 1605. The valves are both latchingtype valves with a single actuator 1602 a or 1603 a for each valve, formoving the valve to either the open or closed position when the valve isunlatched. When valve 1602 is in the open position, it connects a source1606 of pressurized hydraulic fluid to the hydraulic cylinder 1601 viapump 1607. When valve 1603 is open, it connects cylinder 1601 to a sump1607. Electrical signals for energizing the actuators 1602 a and 1603 aare supplied to the respective actuators via lines 1607 and 1608 from acontroller 1609, which in turn may be controlled by a central processor,if desired. The controller 1609 receives input signals from a pressuretransducer 1610 coupled to the hydraulic cylinder 1601 via line 1611.The accumulator 1604 is coupled to the hydraulic cylinder 1601 through avalve 1612, as described in more detail below.

FIG. 34B is a schematic diagram of a modified version of the system ofFIG. 34A to provide both rebound damping and compression damping. Theonly difference is that the system of FIG. 34B includes a valve 1613between the accumulator 1603 and the compression side of the hydrauliccylinder 1601, so that the accumulator 1603 provides compression dampingwhen the rod of the cylinder 1601 is moved from right to left in FIG.34A.

FIGS. 35A and 35B illustrate systems that are identical to those ofFIGS. 34A and 15B, except that the latching valves are replaced withnon-latching valves 1702 and 1703. Elements 1701, 1704, 1705, 1706,1707, 1708, 1709, 1710, 1711, 1712, and 1715 are similar tocorresponding elements 1601, 1604, 1605, 1606, 1608, 1609, 1610, 1611,1612, and 1615 of FIG. 34A. Referring back to FIG. 35B, the non-latchingvalves 1702 and 1703 are biased toward their closed positions byrespective springs 102 a and 1703 a, and can be moved to their openpositions by energizing their respective actuators 1702 b and 1703 b.

In the control system of FIG. 34B, a PWM control system may be used tosupply short-duration pulses P to the actuators 1602 a or 1603 a of thecontrol valves 1602 or 1603 to move the selected valve to its openposition for short intervals corresponding to the widths of the PWMpulses. This significantly reduces the energy required to increase ordecrease the pressure in the hydraulic cylinder 1601 for adjusting thedown pressure on the soil-engaging implement. As depicted in FIG. 36,pulses P1-P3, having a voltage level V1, are supplied to the actuator1602 a when it is desired to increase the hydraulic pressure supplied tothe hydraulic cylinder 1601. The first pulse P1 has a width T1 which isshorter than the width of pulses P2 and P3, so that the pressureincrease is smaller than the increase that would be produced if P1 hadthe same width as pulses P2 and P3. Pulses P4-P6, which have a voltagelevel V2, are supplied to the actuator 1602 a when it is desired todecrease the hydraulic pressure supplied to the hydraulic cylinder 1601.The first pulse P4 has a width that is shorter than the width T2 ofpulses P2 and P3, so that the pressure decrease is smaller than thedecrease that would be produced if P4 had the same width as pulses P5and P6. When no pulses are supplied to either of the two actuators 1602a and 1603 a, as in the “no change” interval in FIG. 36, the hydraulicpressure remains substantially constant in the hydraulic cylinder 1601.

While particular embodiments and applications of the present inventionhave been illustrated and described, it is to be understood that theinvention is not limited to the precise construction and compositionsdisclosed herein and that various modifications, changes, and variationscan be apparent from the foregoing descriptions without departing fromthe spirit and scope of the invention as defined in the appended claims.

The invention claimed is:
 1. A hydraulic control system for controllingthe down force on an agricultural implement, comprising a hydrauliccylinder containing a ram, a source of pressurized fluid coupled to saidhydraulic cylinder on a first side of said ram by a first controllablevalve, a fluid sump coupled to said hydraulic cylinder on said firstside of said ram by a second controllable valve, an electricalcontroller coupled to said first and second controllable valves foropening and closing said first and second controllable valves, a pair ofenergy storage devices coupled to said hydraulic cylinder on oppositesides of said ram, and a check valve coupling said hydraulic cylinder toat least one of said pair of energy storage devices.
 2. The hydrauliccontrol system of claim 1 which includes a second check valve couplingsaid hydraulic cylinder to said first and second controllable valves. 3.A hydraulic control system for controlling the down force on anagricultural implement, comprising a hydraulic cylinder containing aram, a source of pressurized fluid coupled to said hydraulic cylinder ona first side of said ram by a first controllable valve, a fluid sumpcoupled to said hydraulic cylinder on said first side of said ram by asecond controllable valve, and an electrical controller coupled to saidfirst and second controllable valves for opening and closing said firstand second controllable valves, a pressure transducer coupled to saidhydraulic cylinder on one side of said ram, a down pressure controllerfor controlling the down pressure on at least a portion of theimplement, and a load sensor comprising a mechanical element mounted formovement in response to the downward force applied to the implement, afluid-containing device containing a element coupled to said mechanicalelement for changing the fluid pressure in response to the movement ofsaid mechanical element, and a transducer coupled to saidfluid-containing device for producing an output signal in response tochanges in said fluid pressure.
 4. The hydraulic control system of claim3 which includes an energy storage device coupled to saidfluid-containing device for receiving a limited amount of fluid inresponse to changes in said fluid pressure to damp pressure spikes inthe output signal of said transducer.
 5. The hydraulic control system ofclaim 4 in which said energy storage device is an accumulator receivingpressurized fluid from said fluid-containing device, said accumulatorcontaining a element responsive to the pressure of the fluid receivedfrom said fluid-containing device.